bump version to 3.9.1

Author: crossle

app/build.gradle

@@ -18,7 +18,7 @@ plugins {
 def versionMajor = 3
 def versionMinor = 9
 def versionPatch = 1
-def versionBuild = 0
+def versionBuild = 2
 
 apply plugin: 'com.google.gms.google-services'
 apply plugin: 'com.google.firebase.crashlytics'